This application claims priorities to Japanese patent application serial numbers 2002-069149 and 2002-178991, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to impeller pumps of a type known as Westco pumps, generative or friction pumps, cascade pumps and circumferential-flow pumps that have rotary impellers. In particular, the present invention relates to impeller pumps that are suitably used as fuel pumps for vehicles, e.g. automobiles.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 3-18688 teaches a know Westco pump that includes a pump casing and an impeller rotatably disposed within the pump casing. A plurality of grooves are formed in the outer periphery on each side of the impeller and are arranged in the circumferential direction. The pump casing defines a pump chamber that opposes to the grooves. An inlet port and an outlet port are defined in the pump casing and communicate with the pump channel.
In general, when low noise pumps are desired, Westco pumps are chosen due to their low noise properties in comparison with displacement-type pumps, e.g., gear pumps, vane pumps and trochoid pumps. When a pump is operated, a fluid with pulsation in pressure is discharged from the pump. As for Westco pumps, pulsation of a fluid discharged from Westco pumps may appear as a periodical-variation in flow rate (an alternative component or a variation component) that is superposed on a uniform flow rate (a linear component or a constant component). Therefore, Westco pumps may produce relatively low noises in comparison with displacement-type pumps as described above.
However, known Westco pumps still generate noises due to periodical variation in flow rate that may be caused by the nature of impellers that have vane grooves or vanes spaced from each other in the circumferential direction.
In addition, due to recent demands for low-noise automobiles, there has been a strong demand for low-noise impeller pumps that are used as fuel pumps for automobiles.
It is accordingly an object of the present invention to teach improved techniques for reducing or minimizing noises from impeller pumps.
According to one aspect of the present teachings, impeller pumps are taught that may have at least one pump chamber each including a first chamber and a second chamber. An impeller may be rotatably disposed within the pump chamber. The impeller may have a first groove group and a second groove group on opposite surfaces. The first groove group and the second groove group may oppose to the first chamber and the second chamber, respectively, so that a fluid is draw into and discharged from the first and second chambers as the impeller rotates. The flows of the fluid discharged from the pump chambers may have pulsations that are canceled each other when the flows of the fluid are converged at the converging channel.
Therefore, noises that may be produced due to pulsations of the fluid may be reduced or minimized.
According to another aspect of the present teachings, the pulsations of the fluid may be cancelled by determining the relative positions of the first groove group and the second groove group in the circumferential direction and/or the relative positions of outlets ports of the first and second chambers.
According to another aspect of the present teachings, the outlet ports of the first and second chambers may be positioned at the same position in the circumferential direction. On the other hand, the first groove group and the second groove group may be offset from each other by a distance that may correspond to a pitch of the grooves in the circumferential direction divided by the number of the groove groups. For example, if the pump includes a single pump chamber, the first groove group and the second groove group may be offset from each other by a distance that may correspond to half the pitch of the grooves. As a result, the phases of pulsations of the fluid from the first and second chambers may be shifted from each other by a cyclic period of the pulsations divided by the number of the groove groups. Therefore, the pulsations may be canceled when the flows of the fluid from the first and second chambers converged at the converging channel.
According to another aspect of the present teachings, the first groove group and the second groove group may be positioned at the same position in the circumferential direction. On the other hand, the outlet ports of the first and second chambers may be offset from each other by a distance that may correspond to a pitch of the grooves in the circumferential direction divided by the number of the groove groups. For example, if the pump includes a single pump chamber, the outlet ports may be offset from each other by a distance that may correspond to half the pitch of the grooves. As a result, the phases of pulsations of the fluid from the first and second chambers may be shifted from each other by a cyclic period of the pulsations divided by the number of the groove groups. Therefore, the pulsations may be canceled when the flows of the fluid from the first and second chambers converged at the converging channel.
According to another aspect of the present teachings, the first groove group and the second groove group may be offset from each other in the circumferential direction. In addition, the outlet ports of the first and second chambers also may be offset from each other. The offset distances may be appropriately determined in response to the number of the groove groups.
According to another aspect of the present teachings, the first chamber and the second chamber communicate with each other, so that the pressure within the first chamber and pressure within the second chamber may be balanced with each other. As a result, the pulsations in the discharged fluid may be further reduced or minimized.
According to another aspect of the present teachings, the fluid is a fuel that is supplied to an automobile engine. Therefore, the pump may be configured as a low noise fuel pump that is advantageously incorporated into an automobile in order to reduce noises.